Magnetic control device



a May 12, 1959 s. H. DEWITZ 2,886,789

. MAGNETIC conmor. DEVICE Filed Sept. 18. 1952 c E SOURCE OF "222% gm?F'Gn 3. Q 40 36 /30 v 40 INVENTOR GER/MED H. DEW/TZ ATTORNEYS UnitedStates Patent MAGNETIC CONTROL DEVICE Gerhard H. Dewitz, Westport,Conn., assignor to C. G. S. Laboratories, Inc., Stamford, Conn., acorporation of Connecticut Application September 18, 1952, Serial No.310,341

Claims. (Cl. 336-155) This invention is in the field of high frequencysaturable core magnetic apparatus in which the inductance of a signalwinding is controlled electrically by varying the magnitude of a currentsent through a control windmg.

In such controllable inductors, sometimes called saturable reactors, thecontrol and signal windings are wound on a common ferromagnetic core.Variation in the current flowing thru the control winding changes thedegree of magnetic saturation of the core and so varies the effectiveinductance of the signal winding. Thus, the magnitude of an alternatingcurrent passed through the signal winding can be controlled inaccordance with variations produced in the unidirectional controlcurrent flowing through the control winding.

Such devices have been used largely for low frequency applications:their high losses and slow response time have prevented higher frequencyapplications.

The development of ferromagnetic ceramic core materials, as described bySnoeck in U.S. Patents 2,452,529; 2,452,530; and 2,452,531, haspermitted higher frequency operation. Controllable inductors using suchceramic materials are described in my copending applications Serial Nos.213,548 and 278,069 filed March 2, 1951 and March 22, 1952, repectively.The latter has now issued as Patent No. 2,820,109 dated January 14,1958. Those devices are provided with ring cores having a rectangularopening or hole through the rim through which two portions of the signalwinding, are wound. An alternating signal current to be controlled ispassed through these two portions of the signal winding in such manneras to produce signal flux lines encircling this opening. Thisapplication is a continuation-in-part of both of these earlierapplications.

By means of the present invention the upper frequency limit ofcontrollable inductors is still further extended, the control current isrendered more etfective, and the isolation of the control and signalwinding is further improved.

In connection with one aspect of the invention, the magnetic saturationof the flux path of the signal wind-- ing is maintained substantiallyuniform throughout its length. This is important because the signal fluxtends to spread into those portions of the core having lower saturationand therefore higher effective permeability- Generally speaking, thelosses in ferromagnetic ceramic material are higher when the magneticsaturation is low: accordingly, any core areas of low saturationrepresent areas having increased losses. If the signal winding is usedin a resonant circuit, maximum saturation of the core occurs at thehighest frequencies: accordingly, any portion of the flux path of thesignal winding that is at low saturation increases the losses at thesehigher frequencies, reducing the Q of the signal winding and reducingthe upper frequency limit.

The cores are formed with reduced cross sectional areas adjacent bothsides of the signal winding opening or 2,886,789 Patented May 12, 1959openings in order to provide pre-saturation or magnetic isolationregions at these locations. These isolation regions act to restrict anddirect the path of the control saturation flux so as to cause it to passthrough substantially the entire core material closely adjacent theopening. Thus the saturation flux has a maximum effectiveness inrelation to the closed path of the signal winding flux passing aroundthis opening. Moreover, these pre-saturation regions act to confine thesignal winding flux to these same portions of the core, whereby when thecontrol flux is at its maximum saturation value, the signal flux isconfined to portions of the core which are substantially fullysaturated.

Z have found that by forming the core in this manner, the effectivevalue of the Q of the ferromagnetic ceramic material used is raised athigh frequencies so that magnetic apparatus made according to myinvention can be used at frequencies hitherto unobtainable in suchapparatus using ferromagnetic core material. For example, with myinvention the upper frequency limit of ferromagnetic ceramic materialsis increased many fold.

Irrespective of whether the cores are composed of ceramic material, someimprovements are experienced by using this invention with other corematerials having somewhat similar magnetic characteristics. For example,the action of the control current is rendered more effective and theisolation of the signal windings from the control windings is increased.

These and other objects, aspects, and advantages of the presentinvention will be in part pointed out and in part apparent from theaccompanying drawings, in which:

Figure 1 of the accompanying drawings shows a controllable inductorembodying the present invention;

Figure 2 is an enlarged partial elevational view of the signal windingcore portion and adjacent portions of the core of the inductor of Figure1 with the windings omitted to show the relationships more clearly;

Other core forms are illustrated in the partial elevational views of thesignal winding portions and neighboring portions of cores shown inFigures 3 to 7 in which the windings have been omitted from the cores inorder to illustrate more clearly the differences therebetween.

Figure 3 is a view of a rectangular signal winding core portion withrectangular flux control notches adjacent the opening;

Figure 4 shows the reduced cross-sectional area or flux control regionextending a relatively large distance on either side of the signalwinding hole;

Figure 5 shows another core form with staggered indentations adjacentthe signal winding hole;

Figure 6 shows still another form of the region of fluxcontrol reducedcross sectional area, the core being formed from two pieces fittedtogether along its center line; and

Figure 7 illustrates more than one signal winding portion formed on thesame core.

The inductor, generally indicated at 2, in Figure 1, includes a ringcore 4 having a form similar to that shown in Figure 9 of my copendingapplication, Serial No. 278,- 069, now Patent No. 2,820,109, asmentioned above. This core is composed of a ferromagnetic ceramicmaterial as described above or core materials having somewhat similarmagnetic characteristics. I have found that these ceramic materialsotfer marked advantages because of their high effective Qs, their highinitial permeability, their relatively low saturation threshold and wideoperating range, etc. Moreover, these materials apparently exhibit theproperty discussed above that within a range at high frequencies theirlosses decrease with increase in magnetic saturation.

The ring core 4 has a first portion of substantially uniform crosssectional area around which is located the con- 3 a trol winding 6,usually having a relatively large number of turns. However (see Figure2), between the broken lines 7 and 8, is located the signal winding coreportion in which by following the core from the region of either theline 7 or 8 toward the center of a signal Winding opening 9 it is seenthat the cross sectional area of the core is first gradually and thenprogressively more abruptly decreased by means of pairs of curvedindentations 10A and B, and 11A and B. These curved indentations formtwo throats or flux control regions, generally indicated at 12 and 14,near both sides of the transverse signal Winding opening 9, whichaccommodates the signal winding, generally indicated at 18 (see Figurel).

The control winding 6 is connected to a suitable source of controlcurrent diagrammatically indicated at 20, and the degree of magneticsaturation of the entire core is controlled by the current flowingthrough winding 6 in a manner well known in the art of saturable coremagnetic apparatus. The control flux produced thereby flows in a closedpath through the core 4, for instance, it may flow through the signalwinding portion in the direction of the arrows 22 shown in Figure 2.

In order to reduce the undesired magnetic coupling be tween the controlWinding 6 and the signal winding 18, the latter is formed into two equalsections 18-1 and 18--2. These sections are wound through the transversehole 9 and around spaced rim or branch portions 24 and 26 of the core 4,which pass around opposite sides of the hole 9. The sections 181 and18-2 are connected in series in such a direction that signal flux linesformed by current flowing from the controlled circuits, diagrammaticallyindicated at 28, through the winding 18 travel in a closed path aroundthis hole, passing through the lengths of core branches 24 and 26.

In order to confine the path of the saturation flux 22 and to direct italong the lengths of the core branches 24 and 26 so that it regulateswith maximum efficiency the saturation of substantially all portions ofthe magnetic material adjacent the hole 9, I provide the pairs ofindentations 10A and B and 11A and B to form the narrow flux controlthroats or presaturation regions 12 and 14 of relatively abruptlyreduced cross sectional area closely adjacent each end of the hole 9.

These pairs of indentations are symmetrically formed to left and rightof the center of the opening 9, and they are similar above and below thelongitudinal central axis of the core. Each indentation is formed withcurved side Walls, which as seen in Figure 2 conform to a circular areover a substantial portion of their length. For instance, the depression10A has a convex arcuate side beginning at the dotted line 7 andextending down toward the throated region 12, where it merges with thebottom of the depression which is rounded with a concave curve. Theresulting general pattern of the saturation flux around the hole 9 isindicated by the arrows 22. As mentioned above, the alternating signalflux caused by the high frequency signal currents flowing in the winding18, passes in a closed path around this hole and is regulated by themagnitude of the control flux 22. The action of these presaturationthroat regions 12 and 14 in confining the saturation flux 22 and,moreover, in providing additional isolation of the signal winding 18from the control Winding 6 is explained below.

During operation, the current through the control winding 6 is varied inorder to vary the inductance of the signal winding 18. When the controlcurrent is very small, the portions of the core 4 surrounding the hole 9have a low control flux density, so that their permeability to thealternating signal flux is high. Hence, the inductance of the winding 18is large. As the control flux 22 is increased, the degree of saturationof the signal flux path around the hole is increased, thus decreasingthe permeability of this path and hence decreasing the inductance of thewinding 18. At maximum value of the control flux 22, substantially theentire signal flux path around the hole 9 is 4 fully saturated, and theinductance of the winding 18 is at a minimum.

The tendency of the signal flux is to spread out away from the hole andpass through those regions of lowest reluctance or highest permeabilityneighboring thereto. That is, in the absence of the restrictedpre-saturation throat regions 12 and 14, the signal flux would tend toloop out on each side of the hole 9 toward thedotted lines 7 and S forthese portions of the core 4 have lower average values of saturatingflux than most regions of the core adjacent the hole. Thus, in theabsence of restrictions 12 and 14, as the signal flux path is furtherand further saturated, the signal flux would have a greater and greatertendency to spread away from the desired path around the hole 9. Theresult of this tendency of the signal flux to pass into regions of lowersaturation, which occurs in variable inductors as they are now known inthe art, is to prevent the maximum control of the signal flux by theareas saturated by the control flux. The presence of the presaturationregions 12 and 14 restricts the control flux 22 to a relatively smallcross sectional area at these locations. Hence, as the control fluxincreases, the pre-saturation areas are among the first areas toapproach the threshold of saturation, and consequently theirpermeability is forced down, confining the signal flux to the corematerial in the branches 24 and 26 and at each end to material adjacentthe hole. Thus, the signal flux is isolated from portions of the corecarrying the control winding 6 and travels a closed path closelyadjacent the hole where it is very effectively controlled. by the flux-22, to produce a low value of minimum inductance.

In addition to providing isolation and highly effective control action,the pre-saturation regions 12 and 14 force the signal flux to traversecore material, which, in the low inductance range (which is often thehigh frequency range), is substantially all fully saturated. It is acharacteristic of this ceramic material that in this high frequencyrange the losses in the material decrease with increasing magneticsaturation. That is, within certain ranges losses are a direct functionof permeability. In cores embodying the present invention the signalflux is forced to travel in low loss areas of high saturation, as theinductance of the signal winding is decreased, thus providing extremelyhigh Q, high frequency operation.

The relationships between the pre-saturation throats or isolation areas12 and 14 and the dimensions of the branches 24 and 26 as they affectthe operation of the unit 2 are as follows. I have found that for manyapplications it is preferable to have the cross sectional areas at 12and at 14 each slightly less than the sum of the cross sectional areasof the branches 24 and 26. For example, the cross-sectional area at A isusually around to of this sum. Also, the maximum width of the core nearthe signal winding opening is considerably greater than the width of thethroats 12 and 14.

A further reduction in the cross-sectional areas of the pre-saturationregions provides an even greater isolation effect, which may bedesirable in some applications, where the added reluctance in thecontrol circuit is acceptable. When the areas of the pre-saturationregions are increased from this 80 to 90% value, the reluctance of thecontrol circuit is decreased so that less control current is required;however, there is some loss in effective Q. For example, I have foundthat for lower frequency operation, and in certain variable frequencyoscillator applications, lower Q values are acceptable.

In Figure 3 is shown another embodiment of the present invention inwhich the core 30 is provided with a rectangular opening 32 and a pairof straight-sided slots near each end thereof to provide pre-saturationor isolation regions or throats 34 and 35. An advantage of this form ofcore is that a relatively larger opening 32 is available to receive thesignal winding without any increase in the overall core dimensions. Withthis form it is preferable to have the cross-sectional area of each ofthe throats 34 and 35 approximately equal to the sum of thecross-sectional areas of each of the branches 36 and 37.

It should be noted that the form of signal winding core portion shown inFigures 2, 5, 6, and 7 has a transition range in the pre-saturationregion wherein the rate of reduction of cross sectional area of the coreas seen by progressing along the core toward the center of the signalwinding opening is more or less first gradual and then becomes moreabrupt. For example, in Figure 2 it is seen, by following the core fromthe dotted line 7 toward the opening 9, that there is a transition rangein which the cross sectional area is more or less gradually reducing,and then it more abruptly reduces to the narrowest portion of the throat12. Although the form shown in Figure 3 is satisfactory for manyapplications, I prefer the use of a transitional range as yielding ahigher effective Q in the higher frequency ranges.

In Figure 4 is shown in elevation a portion of a ring core 38 with asmall annular signal winding core 39 formed integral therewith andhaving branches 40 and 41 surrounding the hole 42. In this embodimentthe main core 38 has regions 44 and 46 of reduced uniform crosssectional area which extend all the way around the core 38. Also, thecross sectional area of the core 38 may be increased a portion of theway around in order to reduce the reluctance of the control flux path.Because the regions of reduced cross sectional area extend forconsiderable distances on either side of the hole 42, they provideextensive presaturation throats of a width which is considerably lessthan the maximum width measured across the annular core portion 40. Thecross sectional area of the main ring core 38 in regions 44 and 46 maybe approximately equal to the sum of the cross sectional areas of thebranches 40 and 41, thus being somewhat wider than the throat regions inother figures of the drawings.

In Figure is shown a ring core 48 having a signal winding hole 49 with apair of curved single indentations 5t and 51 on each side thereof. Byprogressing along the core 48 from either side toward the hole 49, it isseen that there is first a gradual and then an abrupt reduction in thecross sectional area of the core 48 on each side of the hole 49 to formthe pre-saturation regions, generally indicated at 52 and 54. Anadvantage of this form of core is that the number of indentations isreduced, while their staggered symmetrical relationship equalizes thereluctance of the magnetic circuits through the core material 48 andalong the two sides of the hole 50.

The core shown in Figure 6 is similar to the core shown in Figure 4 ofmy co-pending application, Ser. No. 213,548, mentioned above. Itcomprises a first core portion 56 of relatively large and uniform crosssection for receiving the control winding, and providing a lowreluctance path for the control flux. Between the dotted lines 58 and 60the core tapers to a smaller cross sectional area and then abruptlyreduces at the pairs of notches 62A and B and 64A and B adjacent asignal winding hole 66. Each of these tapering regions and these notchesprovides an isolation or pre-saturation region adjacent the hole 66,generally indicated at 68 and 70, respectively. Two branches 72 and '74pass by either side of the hole 66. The maximum distance across the coreadjacent the hole 66 is significantly less than the width of the firstportion 56. On the branches 72 and 74 the two portions of the signalwinding are placed. Since with this configuration the cross sectionalarea of the first core portion 56 can be relatively greater for a givensize of signal winding, the reluctance to the control flux isconsiderably reduced, while at the same time an effective control actionis obtained.

In order to facilitate in the fabrication, the core may be formed fromtwo sections which are mirror symmetrical and placed together along thecenter parting line 76.

6 This core may also be formed from a single integral core piece.

The partial elevational view of the core 78 in Figure 7 shows two spacedsignal winding openings 80 and 82. Adjacent each of these openings arepairs of valley-shaped indentations 84A and B and 86A and B, and 88A andB and 90A and B, respectively, which are similar to those use in formingthe core 4, as shown in Figure 2. Each of these indentations is curvedand has a gradually increasing slope toward its center to formpro-saturation and isolation regions adjacent each side of the openings80 and 82. Thus, with the use of the principles shown in the core 78 asingle control winding can be used to control the inductance of two, ormore, signal windings, and because of the formation of thepre-saturation and isolation regions, each of these inductances issubstantially entirely independent of the other controlled windings onthe same core and has no undesired mutual coupling with the controlwinding.

Although only one or two signal winding openings are shown, it isunderstood that by using the principles of this invention a largernumber of independent controlled inductances capable of high efiiectiveQ, high frequency operation can be utilized on one ring core.

It is to be understood that the principles set forth above in connectionwith single ring cores apply equally well to multiple ring corestructures using two or more cores.

From the above description it will be apparent that the saturable coremagnetic units embodying the present invention are well adapted toattain the ends and objects set forth herein and that the variousembodiments of the invention shown herein can be modified so as toproduce operating characteristics best suited to the needs of eachparticular use.

I claim:

1. A core of ferromagnetic material having a first closed magnetic paththerein and a transverse opening therein dividing said first magneticpath into first and sec- 0nd spaced magnetic branches passing on eitherside of said transverse opening and forming a second closed magneticpath passing around said opening, said core having a pair of throatportions of reduced cross sectional area adjacent to opposite sides ofsaid transverse opening, said throat portions each having a smallercross-section than the total cross-section measured directly across saidfirst and second spaced branches and said throat portions each having asignificantly smaller width than the maximum width of said core asmeasured directly across said first and second spaced branches.

2. A core of ferromagnetic material defining a first substantiallyclosed flux path, said core having a first por tion with a transverseopening therein dividing said first flux path into first and secondspaced magnetic branches passing along opposite sides of said opening,said branches defining a second substantially closed flux path passingaround said opening, said core having a pair of throat portions formedtherein, said throat portions being adjacent to opposite sides of saidfirst portion and being spaced a short distance from opposite ends ofsaid transverse opening and each having a substantially less width thanthe maximum width of said core as measured directly across said firstand second branches, the cross sectional area of each of said throatportions being approximately equal to the sum of the cross sectionalareas of each of said separate branches.

3. A variable induction apparatus comprising magnetic core means havinga first closed magnetic flux path therein, a first winding surrounding aportion of said core means and magnetically coupled to said first closedflux path, a transverse opening in said core means dividing said firstclosed path into first and second spaced branches passing on oppositesides of said opening and forming parallel branches in said first fluxpath, and a second winding having first and second portions woundthrough said opening and respectively around said spaced branches, asecond closed magnetic flux path for said second winding passing aroundsaid opening, said core means defining first and second pairs of opposedindentations near the opposite ends of each of said branches the minimumWidth of said core means at each pair of indentations beingsubstantially less than the maximum width of said core means measureddirectly across said first and second spaced branches, the minimum crosssectional area of said core means at said pairs of indentations beingnot significantly greater than the sum of the minimum cross sectionalareas of said first and second spaced branches, said pairs ofindentations deflecting said first path at the opposite ends of saidtransverse opening so as to pass through substantially all portions ofthe core material adjacent said transverse opening whereby the degree ofsaturation along substantially all of sad second closed flux path isefiectively controlled and said second winding has a high eifective Q athigh operating frequencies.

4. A controllable inductance apparatus comprising magnetic core meansdefining a first closed magnetic flux path therein, a first windingsurrounding a portion of said core means arranged to induce magneticflux in said first closed path, a transverse opening in said core meansdividing said first path into first and second spaced branches passingon opposite sides of said opening and defining a second closed magneticflux path passing around said transverse opening and through said firstand second spaced branches, a second winding having first and secondportions wound through said opening and respectively around said spacedbranches, said core means including a pair of pre-saturation regions ofabrupt reduction in width near opposite ends of said branches, saidpre-saturation regions having a minimum width substantially smaller thanthe maximum Width measured directly across said first and second spacedbranches, said core means in said pre-saturation regions having a crosssectional area less than the sum of the cross sectional areas of saidfirst and second spaced branches, said pre-saturation regions causingsaid first flux path to deflect inwardly adjacent to opposite ends ofsaid transverse opening so as to travel substantially the entire wayaround said transverse opening, and a transition region included in saidcore means adjacent each of said pre-saturation regions, the crosssectional area of the core means relatively gradually and progressivelydecreasing in said transition region in a direction toward saidpre-saturation region, said transition regions being spaced further fromsaid transverse opening than said pre-saturation regions.

5. A controllable inductance apparatus as claimed in claim 4 and whereinthe cross sectional area of the core means in said pre-saturationregions is in the range from about 80% to about 90% of the sum of thecross sectional areas of said first and second spaced branches.

6. A controllable inductance apparatus comprising core means offerromagnetic material having a first portion of approximately uniformcross sectional area and a second portion with a small transverseopening therein defining a pair of spaced branch portions passing aroundopposite sides of said opening each of said branch porlions having asubstantially equivalent cross sectional area, said first and secondcore portions defining a closed path for magnetic flux, and defining alarge opening with said closed path passing around said opening andthrough said first and second core portions, a first winding passingthrough said large opening and around said first portion and a secondWinding having first and second portions wound through said transverseopening and respectively around said opposite branch portions, said coremeans defining first and second opposed pairs of indentations thereinnear opposite ends of said transverse opening, the Walls of each of saidindentations over a major part of their length as seen in elevationbeing arcuate and convex, the minimum widths of said core means asmeasured at the narrowest points under said opposed pairs ofindentations near opposite ends of said transverse opening beingsubstantially less than the maximum distance across said transverseopening between the outside surfaces of said respective branch portions,and the cross sectional areas of said core means as measured at thenarrowest points under said opposed pairs of indentations beingapproximately equal to the sum of the cross sectional areas of said pairof spaced branch portions.

7. A core of ferromagnetic material having a first closed magnetic paththerein and a rounded transverse opening therein dividing said firstflux path into a pair of branch paths of substantially equivalent crosssectional area passing on opposite sides of said opening, said coreforming a second closed magnetic path passing around said opening andthrough said branch paths, and a winding having first and second equalportions wound through said transverse opening and respectively aroundsaid opposite branch paths and serially connected in the same directionwith respect to said second path, said core having indentations abruptlydecreasing its cross sectional area adjacent opposite ends of saidbranch paths to an area less than the sum of the cross sectional areasof said branch paths, said indentations being spaced from said opening,said core having a substantially larger cross sectional area commensingat the extreme limits of said indentations and extending for substantialdistances away from each of said indentations.

8. A variable inductance apparatus comprising a magnetic core having afirst substantially closed flux path therein, a first windingsurrounding said first path, a transverse opening in said core dividingsaid first path into first and second branches passing on opposite sidesof said opening, a second winding having first and second portions woundthrough said circular opening and respectively around said branches, thecross sectional area of said core as it extends in a direction towardeither side of said transverse opening first gradually and then abruptlydecreasing to a minimum value of from to of the sum of the crosssectional areas of said branches.

9. Controllable inductance apparatus comprising magnetically permeablecore means defining a first closed path for magnetic fiux, a firstwinding on said core means passing around said first path, said coremeans including a transverse opening therein and dividing said firstpath into first and second spaced magnetic branches extending alongopposite sides of said transverse opening and defining a second closedpath for magnetic flux passing around said transverse opening andthrough said first and second spaced magnetic branches, a second Windinghaving first and second parts passing through said transverse openingand around said first and second spaced magnetic branches, respectively,said parts of said second Winding being interconnected in series aidingrelationship with respect to the flux passing around said transverseopening, said core means having indentations near opposite ends of saidtransverse opening and adjacent to opposite ends of said spaced magneticbranches, the cross sectional areas of said core means measured at thebottom of said indentations and adjacent to the opposite ends of saidspaced magnetic branches being less than the to: tal cross sectionalarea as measured directly across said spaced magnetic branches and thewidths of said core means measured at the bottom of said indentationsand adjacent to opposite ends of said spaced magnetic branches beingsubstantially less than the maximum overall width of said core meansmeasured from the outside surface of said first magnetic branch to theoutside surface of said second magnetic branch.

10. Controllable inductance apparatus comprising magnetically permeablecore means defining a first closed path for magnetic flux, a firstwinding passing around said first path, said core means including afirst portion having a transverse opening passing therethrough anddividing said first flux path into first and second spaced magnetic 9branches passing on opposite sides of said opening, said first coreportion defining a second substantially closed flux path passing aroundid opening and through said first and second spaced magnetic branches, asecond winding having first and second parts passing through saidtransverse opening and respectively around said first and second spacedmagnetic branches, said parts of said second winding beinginterconnected in the same sense With respect to flux passing aroundsaid transverse opening in said second path, said core means including apair of throat portions in said first flux path and adjacent to 0ppositeends of said branches, each of said throat portions having asubstantially smaller minimum width than the over-all Width of saidfirst core portion measured directly across from the outside of saidfirst branch to the outside of said second branch, said throat portionseach having a cross sectional area which is substantially equal to the10 sum of the cross sectional areas of said first and second spacedmagnetic branches, said throat portions converging the flux in saidfirst path at opposite ends of said transverse opening, whereby the fluxin said first path passes along substantially the entire length of saidsecond path.

References Cited in the file of this patent UNITED STATES PATENTS

